1. Field of the Invention
The present invention relates to a system and method for self diagnosing a magnitude of deterioration of an engine controlling system, such as an ignition system, a fuel injection system, and/or EGR (Exhaust Gas Recirculation) control system applicable to an automotive IC (Internal Combustion) engine using a cross-correlation function derived from functions of a periodic pseudo random signal and an output signal related to deterioration of the engine controlling system.
2. Description of the Background Art
An ignition system has been put into practice which carries out ignition of an air-fuel mixture supplied to each cylinder of the engine.
The ignition systems generally include a vehicular battery, an ignition coil, a plurality of ignition plugs, each installed so as to be exposed to a corresponding combustion chamber, and a power transistor which turns on and off a primary current of the ignition coil. When the primary current flowing through the primary winding of the ignition coil is interrupted at a time when a cylinder piston reaches a predetermined angular position before top dead center (BTDC) in each compression stroke, a high surge voltage is generated across a secondary winding of the ignition coil, the high surge voltage being supplied to one of the ignition plugs of the corresponding cylinder in the compression stroke. At this time, the ignition plug is sparked to ignite the air-fuel mixture supplied into the corresponding combustion chamber.
It is noted that, for a six-cylinder engine, an ignition signal (pulse signal) supplied to a base of the power transistor has its falling edge at a timing of which is the ignition timing and a time duration during which the power transistor is in the ON state is defined as a, so-called, dwell angle, i.e., a duration of time during which the power transistor continues to turn on (primary current is flowing through the primary winding).
A control unit of the ignition system controls both ignition timing and dwell angle according to an instantaneous engine driving condition. The control unit is constituted by a microcomputer.
Deterioration of the ignition system tends to accelerate depending on its use environment and, in a worst case, cannot maintain its perdetermined performance although it has durability such that it may continue to function past its useful period of time. For example, if the ignition coil is deteriorated, it becomes impossible to provide a sufficient discharge energy across each ignition plug. Consequently, misfiring tends to occur in the combustion chambers.
To cope with such a situation as described above, it is important to monitor the performance of the ignition system during the driving of the engine before a failure such as breakage in the ignition system occurs and to take appropriate measures when deterioration of the ignition system has been determined.
However, since the ignition system is usually not provided with a function for monitoring its operation, a vehicule driver may continue to operate the vehicle without knowing of the deteriorated ignition system.
It is noted that, although one previously proposed ignition system has detection means for detecting a primary voltage across the ignition coil and determining means for determining that a misfire has occurred when the value of the primary voltage is below a predetermined value, this may be caused by such as breakage, and an input circuit for detecting the primary voltage required. However, this previously proposed system cannot determine if any one ignition plug or plugs have failed even though the ignition coil is normal.
Further, fuel injection systems have been put into practice in order to carry out accurate fuel control under a wide engine operating condition to reduce exhaust gas emission.
A fuel injection system generally includes a fuel tank, a fuel supply pump, a pressure regulator, and a fuel injector installed so as to be exposed toward an intake port of the engine. The pressure regulator serves to maintain a fuel pressure supplied to the fuel injector constant.
The fuel injector has a valve portion which opens only during a flow of current into its solenoid during the opening of which fuel is injected and supplied to the intake port. A quantity of fuel injected from the fuel injector is determined during which the current flows through the solenoid.
The problem described in the case of the ignition system can be applied equally well to a previously proposed fuel injection system.
Furthermore, EGR (Exhaust Gas Recirculation) systems have also been widely put into practice.
An EGR system is installed in the engine in order to return a part of exhaust gas to an intake air system in order to reduce a harmful component of exhaust gas (NOx).
Previously proposed EGR systems include a passage communicated between an exhaust manifold and intake manifold for bypassing the engine, an EGR control valve intervened in the bypass passage, and a negative pressure control electromagnetic valve to produce a controlled negative pressure toward the EGR control valve.
The EGR control valve increases and decreases in opening angle according to the controlled negative pressure introduced into a working chamber of the control valve so that a recirculated quantity (EGR quantity) of the exhaust gas flowing through the bypass passage is controlled.
The negative pressure control electromagnetic valve includes a constant pressure valve portion for providing an intake manifold negative pressure for a constant negative pressure of -120 mmHg and a solenoid valve portion for providing a controlled negative pressure from -15 through -120 mmHg when introducing an atmospheric pressure.
A control signal supplied to the solenoid valve portion is an on-and-off pulse, the control unit determining a pulse duty ratio of the On-and-off pulse (EGR ratio controlled value) according to a driving condition of the engine.
The problem described in the case of the ignition system can be applied equally well to the EGR system.